Not necessarily, you can continually write until you hit the end of the uninitialized data segment, which is typically 128kb (or MMAP_THRESHOLD) after the last

Not necessarily, you can continually write until you hit the end of the uninitialized data segment, which is typically 128kb (or MMAP_THRESHOLD) after the last heap allocation (that itself was under 128kb, otherwise the memory will be, as you state, mmapped, which has no contiguity guarantees)